This is the Baylor College of Medicine (BCM)-University of Texas Medical School in Houston (UT) application for Part III of the Women and Infants Transmission Study (WITS). BCM-UT has been an active participant in WITS II endeavors through award of cooperative agreement U01-AI34840-01 in July 1993. Since 1988, BCM-UT has established liaisons with providers who care for a large maternal-infant population infected with human immunodeficiency virus (HIV). These providers make up National Institutes of Health (NIH)-sponsored Pediatric Obstetrical HIV RESEARCH CENTER at BCM and UT. BCM-UT seeks to continue to perform WITS research as part of its coordinated recruitment of HIV-infected mother-infant pairs into natural history, diagnostic, and therapeutic clinical trial programs. By using the combined strengths of other NIH-funded research, including basic science awards, and the facilities of the General Clinical Research Center (GCRC) at the BCM-affiliated Texas Children's Hospital, it will be possible to continue to enroll 50 mother-infant pairs per year into WITS with greatest economy of financial resources. The following research aims are identified for WITS III: (1) to determine material co-factors related to maternal-infant HIV transmission, including assessment of mechanisms and timing of transmission, (2) to evaluate strategies related to success/failure of perinatal intervention including gestational/postnatal antiretroviral therapy, (3) to determine the impact of pregnancy with/without antiretroviral therapy on the natural history of HIV infection among women through the postpartum period, including immunologic and virologic changes in pregnant HIV-infected women (4) to assess acute HIV infection among both infants and women in light of antiretroviral, prophylactic and immune-based therapy, and (5) to assess factors which might predict disease progression among the cohort of HIV infected children in WITS. Subjects will be recruited through the hospital and clinics affiliated with BCM and UT, private pediatricians and obstetricians in the Houston metropolitan area, and the indigent care clinic system maintained by the Harris County Hospital District Authority. Maternal consent will be obtained after the diagnosis of HIV infection has been documented.